For the production of metal strips, it is possible to utilize continuous working casting machines featuring moving molds (Dr. Herrmann, "Handbuch des Stranggiessens").
Practical application has shown that the speed of the moving molds must be very precisely synchronized with the speed of the strip being cast, in order to avoid relative motion between the originating strip and the surfaces of the moving molds and thereby prevent the occurrence of tension cracks within the solidifying material.
The term mold can apply to any element adapted to form a casting chamber such as revolving metal belts, successive blocks formed of one piece or of a plurality of assembled elements, as well as casting wheels.
In order to create optimal conditions during the casting process, it is therefore necessary that the speed of the molds as well as the speed of the strip being cast be continuously adjustable.
If the casting machine produces a strip having a thickness greater than the dimension which is permissible for the cooling or for coiling off of that strip, it is necessary to roll the cast strip in line and in synchronism with the casting machine.
It is known that the speed of the strip engaged in the rolling process is dependent upon various factors. The practice has shown that even for a given decrease of the thickness and a constant angular velocity of the rolls, the speed of the strip may still experience variations as a function of time.
While it is possible to maintain a practically constant rate of deformation of the strip, practice has shown that it is not possible to maintain a constant value for the coefficient of friction which is dependent upon various factors, nor for the strength or the strain resistance. Both latter values depend for example from the temperature of the strip being rolled, from the rolling speed and from other factors.
Under such conditions, the speed of the strip being rolled may fluctuate several percentages in value over periods of time, even when the peripheral speed or the angular velocity of the rolls remains constant.
For that reason a rigid coupling between the casting machine and the rolling mill is not possible with respect to their individual speed.
At the present it is customary to place pinch rolls at the outlet of the casting machine and to allow for a loop in the cast strip in order to compensate for the speed differences of the strip between the casting machine and the rolling mill. It is also possible to utilize the variations of that loop to produce a signal for controlling the drive of the rolling mill (lecture by R. W. Hazelett and Dr. C. E. Schwartz, American Institute of Mining, 1964, or "Bander, Bleche, Rohre", Issue no 9, 1970, pages 469-471).
The pinch rolls consist of one or several driven pairs of rolls arranged one behind the other in series, which seize the cast strip emerging from the casting machine and guide it under relatively light rolling pressure and at a speed precisely adapted to that of the casting machine, thus eliminating the influence of any forces on the casting machine which act from the outside on the strip, in the direction of casting.
The auxiliary equipment described above requires a relatively great distance between the casting machine and the first rolling mill. This causes a cooling of the cast strip due to radiation of heat and contact with guide rolls. In order to obtain the required temperature for rolling it is usually necessary to place a continuous furnace ahead of the rolling mill to compensate for the heat loss.
Such additional equipment represents a large part of the capital expenditure involved in a casting and rolling plant. Moreover, using the continuous furnace raises the operating expenses besides being in direct contradiction with the general present trend to save energy.
In order to obtain the required precision of regulation of the driving speed of the cast strip to accommodate different equipment arranged in series in the system, the driving speed of the casting machine or the one of the pinch rolls according to the present invention is measured and used as a rated value for controlling the speed of the other elements in the line. For this purpose, there exist already many suitable control devices on the market.